The present invention generally relates to an apparatus for controlling a throttle valve in vehicles. More particularly, the present invention pertains to a throttle valve controlling apparatus that includes a component for electrically controlling the opening of a throttle valve and a component for mechanically controlling the throttle valve when the electric component fails to control the throttle valve.
A typical engine has throttle valve provided in its intake air pipe to control the amount of air drawn into the engine. In one system for controlling the throttle valve opening TA, the throttle valve is coupled to a gas pedal by a wire. The throttle opening TA is mechanically controlled in accordance with the degree of gas pedal depression PA. Therefore, there is a one-to-one relationship between the throttle opening TA and the gas pedal depression amount PA at any given running state of the engine.
Recently, apparatuses for electrically controlling the throttle opening TA have been proposed. This type of apparatus includes a computer for computing a target throttle opening based on the degree of gas pedal depression PA and several parameters indicating the running state of the engine. The computer controls an actuator (for example, an electric motor) of the throttle valve such that the throttle opening TA matches a target throttle opening.
In this type of throttle apparatus, the relationship between the throttle opening TA and the gas pedal depression amount PA is arbitrarily determined. In other words, the throttle opening TA can be altered such that the opening TA is suitable for the running state of the engine, and is not necessarily directly proportional to the degree of pedal depression.
However, when a malfunction occurs in the throttle valve, for example, if the throttle valve sticks to the wall of the intake pipe due to deposits formed in the pipe, the actuator may fail to properly control the throttle opening TA.
Japanese Examined Patent Publication No. 8-23312 discloses an apparatus for dealing with this problem. This apparatus has a mechanical component that couples a gas pedal with to the throttle valve with a wire. When the actuator fails to control the throttle opening TA, the mechanical component takes over the control of the throttle opening TA. FIG. 9 illustrates a throttle valve controlling apparatus that includes such a mechanical component.
This apparatus includes a shaft 81 rotatably supported in an intake air pipe 80, a throttle valve 82 secured to the shaft 81, a motor 83 for controlling the opening of the valve 82, a controller 84, a sensor 85 for detecting the degree of depression of the gas pedal, and a sensor 86 for detecting opening or the throttle valve 82. The controller 84 computes a target throttle opening based on a signal from the gas pedal sensor 85 and actuates the motor 83 such that the throttle opening TA detected by the sensor 86 matches the target opening.
The shaft 81 is secured to a first lever 87, which is urged by a spring 88 in a direction closing the throttle valve 82. A second lever 89, which is rotatably supported on the shaft 81, is coupled to a third lever 91 by a wire 90. Pressing the gas pedal 92 over a predetermined amount causes the pedal 92 to contact the third lever 91 thereby drawing the wire 90. This causes the second lever 89 to contact the first lever 87 and rotates the first lever 87 integrally with the second lever 89 against the force of the spring 88. In this manner, the throttle valve 82 is opened by manipulation of the gas pedal 92.
If the throttle valve 82 sticks to the inner wall of the intake air pipe 80, it is assumed that, even if actuated by the controller 84, the motor 83 will fail to change the throttle opening TA. The controller 84 then judges that the valve 82 is stuck on the inner wall of the pipe 80 and controls the motor 83 to generate the maximum torque. The force of the maximum torque of the motor 83 alone or the combined force of the maximum torque and rotational force applied on the shaft 81 by cooperation of the levers 87, 89 and 91 increases the throttle opening TA. When the increase in the throttle opening TA is detected by the throttle opening sensor 86, the controller 84 judges that the valve 82 is free from the inner wall of the pipe 80. From the time of this judgment, the controller 84 temporarily stops controlling the valve 82 with the motor 83 until the gas pedal 92 is separated from the third lever 91 by the driver's manipulation of the pedal 92.
In this manner, the apparatus frees the throttle valve 82 from the wall of the pipe 80. At this time, the controller 84 stops controlling the throttle valve 82 with the motor 83. Therefore, even if the driver significantly increases the pedal depression PA, the opening TA of the valve 82 is not increased accordingly. This keeps the engine speed lower than the speed that corresponds to the increased amount of pedal depression PA when the valve 82 is actuated by the motor 83.
However, this apparatus has the following drawbacks.
The throttle opening TA is increased for freeing the valve 82 from the wall of the pipe 80. Therefore, when the motor 83 resumes controlling the throttle valve 82 after the valve 82 is controlled by the levers 87, 89 and 91, the vehicle is likely to be moving. This may result in an unpredictable running state of the vehicle.
That is, the same amount of depression of the gas pedal 92 results in different openings of the throttle valve 82 at a time immediately before the motor 83 resumes controlling the valve 82 and at a time immediately after the motor 83 resumes controlling the valve 82. Therefore, if the valve 82 sticks to the pipe 80 and is thereafter freed, the driver may be disturbed due to the unexpected change in the relationship between the degree of depression of the gas pedal 92 and the engine speed.